It is common knowledge that many vehicle occupants often do not use the restraint belt systems with which the vehicles are equipped, either because they are somewhat of a nuisance to connect and disconnect or because the occupants find them to be uncomfortable. It is well established, however, that vehicle occupants are less likely to be seriously injured or killed in a collision if they are restrained by a restraint belt system. One way of increasing the frequency of use of a seat belt system is by making the system "passive", in the sense that the belt is automatically applied to the occupant without his or her intervention whenever the occupant enters the vehicle and closes the door, and similarly, is automatically moved to an inactive or release position when the occupant opens the vehicle door to enter or leave the vehicle. There have been numerous proposals in recent years for passive-type vehicle restraint belt systems. Most of the known passive systems use one or more movable belt transfer guides in the form of either a guide ring or a movable anchor located either inboard or outboard of the vehicle seat, such as at the edge of the roof above the door. The movable belt transfer guide is driven back and forth along a guide rail by a drive device.
U.S. Pat. Nos. 4,365,827 (Dec. 28, 1982) and 4,375,897 (Mar. 8, 1983) issued to the present inventor describe and illustrate passive vehicle occupant restraint belt systems in which a shoulder belt leads from an emergency locking retractor affixed to the vehicle floor inboard of the seat upwardly and outwardly across the seat to a movable belt anchor. The belt anchor is slidable along a guide rail that extends along the edge of the roof above the vehicle door. The belt anchor is moved by a drive wire along the guide rail between a rearward restraint position and a forward release position in response to openings and closings of the vehicle door. The drive wire is a so-called racked wire, which comprises a relatively stiff but bendable core wire element and a rack wire element wound spirally onto the core element and suitably fixed, thus providing a form of rack teeth that are capable of being driven by a special gear which, in turn, is driven by a gear-reduced electric motor or a mechanical linkage associated with the door (e.g., a motion amplifier). The racked wire is suitably fixed to the movable anchor and is constrained by a sheath or guide rail to follow a predetermined path between the drive device and the movable anchor.
Inasmuch as the racked wire cannot be severely bent, for example by winding onto a drum or the like, a tail end of the racked wire on the opposite side of the drive gear from the portion that leads from the drive gear to the belt anchor moves back and forth within a tail-end sheath, the length of which is slightly greater than the distance along the guide rail between the release position and restraint position of the movable anchor. The additional length of racked wire and the casing for the tail-end portion of the racked wire significantly contribute to the cost of production and assembly of the drive device. Moreover, the costs of manufacture of the racked wire itself are comparatively large. Furthermore, the tail-end portion takes up valuable space in the vehicle.
In order to reduce the costs of manufacture and assembly of a passive belt system as well as to reduce the space required by the system, particularly the tail-end portion of a racked wire drive, the present inventor has previously proposed a passive belt system in which the movable belt transfer guide or anchor is driven by a wide, thin flexible band or tape. In particular, as described and shown in U.S. Pat. No. 4,498,690 (Feb. 12, 1985), one end of a perforated tape is connected to the movable guide or anchor of a passive belt system, and the other end is fastened to a drive sprocket wheel having teeth that mesh with the perforations in the tape. Upon rotation of the sprocket wheel in one direction, the flexible drive tape is wound onto the sprocket wheel, pulling the guide member in a direction generally toward the sprocket wheel in the process. Upon rotation in the other direction, the sprocket wheel pushes the tape in a direction to move the movable guide member generally away from the drive device, the tape, of course being unwound in the process.
Although the device of U.S. Pat. No. 4,498,690 is generally satisfactory and constitutes an improvement in many respects over the racked wire drive devices, it is not altogether free from possible problems. One such problem involves the possibility of wear and deterioration of the tape, especially in the regions around the perforations. Also the inherent weakness of the tape at all cross sections corresponding to the perforations makes the tape subject to fatigue failure due to bending at these weak points. Another problem is to provide adequate assurance that the tape is accurately guided away from the sprocket wheel when it is being unwound from the reel such that bending or kinking cannot occur, thereby increasing friction and producing a high load on the drive motor. An object of the present invention is to overcome the aforementioned problems. Another object of the invention is to provide a passive restraint belt system having a drive device that is of simple construction, small size, easy to install and reliable in operation.